1. Field of the Invention
The present invention relates to liquid crystal display (LCD) devices, and more particularly to a method of designing a mask and of fabricating a unit panel while maximizing an efficiency with which a base substrate is used.
2. Discussion of the Related Art
Recent developments within the information communication field have increased demands for various types of display devices. In response to this demand, flat panel displays such as liquid crystal display devices (LCDs), plasma display panels (PDPs), electro luminescent display (ELDs), and vacuum fluorescent display (VFDs) have been developed and use as displays of various products.
Due to their excellent picture quality, light weight, thin profile, and low power consumption, LCDs are used as televisions, capable of receiving and displaying broadcast signals, replacing cathode ray tubes (CRTs), and are widely used in portable displays such as monitors of laptop and notebook computers, video cameras, and the like, that require displays of different sizes.
Despite various technical developments in LCD technology, however, research in enhancing picture quality of LCD devices has been lacking compared to research in other features and advantages of LCD devices. Therefore, to increase the use of LCD devices as displays in various fields of application, LCD devices capable of expressing high quality images (e.g., images having a high resolution and a high luminance) with large-sized screens, while still maintaining a light weight, minimal dimensions, and low power consumption must be developed.
LCDs generally include a LCD panel for displaying a picture and a driving part for providing driving signals to the liquid crystal display panel. The LCD panel generally includes first and second glass substrates bonded to each other and spaced apart from each other by a cell gap. A layer of liquid crystal material is injected into the gap between the first and second glass substrates.
The first glass substrate (i.e., thin film transistor (TFT) array substrate), supports a plurality of gate lines spaced apart from each other at a fixed interval and extending along a first direction; a plurality of data lines spaced apart from each other at a fixed interval and extending along a second direction, substantially perpendicular to the first direction, wherein pixel regions are defined by crossings of the gate and data lines; a plurality of pixel electrodes arranged in a matrix pattern within respective ones of the pixel regions; and a plurality of thin film transistors (TFTs) capable of transmitting signal from the data lines to corresponding ones of the pixel electrodes in response to a signal applied to respective ones of the gate lines.
The second glass substrate (i.e., color filter substrate) supports a black matrix layer for preventing light leakage in areas outside the pixel regions; a color filter layer (R, G, B) for selectively transmitting light having predetermined wavelengths; and a common electrode for implementing a picture. In in-plane switching mode LCD devices, the common electrode is formed on the first substrate.
Uniformity of the cell gap is maintained by spacers arranged between the first and second glass substrates, bonded together by a sealant. The sealant includes a liquid crystal injection inlet allowing liquid crystal material to be injected into the cell gap.
FIG. 1 illustrates a perspective view of a related art LCD panel in a color LCD device.
Referring to FIG. 1, the related art LCD panel includes lower and upper substrates 1 and 2, respectively, that may be bonded together. A layer of liquid crystal material 3 is then injected between the bonded lower and upper substrates 1 and 2.
The lower substrate 1 (i.e., the TFT array substrate) supports a plurality of gate lines 4 spaced apart from each other and extending along a first direction and a plurality of data lines 5 spaced apart from each other and extending along a second direction, substantially perpendicular to the first direction. Pixel regions P are defined by crossings of the gate and data lines 4 and 5, respectively. A plurality of pixel electrodes 6 are arranged in a matrix pattern within respective ones of the pixel regions P and thin film transistors T are formed at crossings of the plurality of gate and data lines 4 and 5, respectively.
The upper substrate (i.e., the color filter array substrate) supports a black matrix layer 7 for preventing light leakage in areas outside the pixel regions P; a color filter layer (R, G, B) 8 for selectively transmitting light having predetermined wavelengths; and a common electrode 9 for implementing a picture.
Each of the thin film transistors T includes a gate electrode protruding from a corresponding gate line 4, a gate insulating layer (not shown) formed over an entire surface of the lower substrate, an active layer formed on the gate insulating layer in a region above the gate electrode, a source electrode protruding from a corresponding data line 5, and a drain electrode formed opposite the source electrode. The pixel electrode 6 is formed of a transparent conductive metal having good light transmittance characteristics such as indium-tin-oxide (ITO).
Still referring to FIG. 1, an orientation of molecules within the layer of liquid crystal material 3, provided between the lower and upper substrates 1 and 2, is adjusted by a signal output by the thin film transistor T. For example, a vertically oriented electric field, generated within the layer of liquid crystal material as a result of the signal output by the thin film transistor T, adjusts the orientation of molecules within the layer of liquid crystal material. When the orientation of the liquid crystal molecules is adjusted, the light transmittance characteristics of the layer of liquid crystal material 3 are affected. Accordingly, the signal output by the thin film transistor T enables the light transmittance characteristics of the layer of liquid crystal 3 to be controlled while providing a pixel region P having a high aperture ratio. The common electrode 9 of the upper substrate 2 is grounded, to prevent the pixel regions P from being electrically damaged.
A method for fabricating the related art LCD panel shown in FIG. 1 will now be explained in greater detail with reference to FIG. 2.
Referring to FIG. 2, a plurality of the aforementioned TFT array substrates or color filter array substrates, both herein referred to as unit panels 12 are formed within a base substrate 11, wherein each unit panel 12 is of the same size. Each unit panel 12 includes an active region 13, a black matrix region 14, and a pad region 15. Unit panels 12 provided as TFT array substrates are fabricated via a plurality of thin film deposition and photolithography steps that incorporate the use of masks. After the unit panels 12 are formed, an inspection is performed to evaluate the quality of the unit panels 12, wherein the unit panel 12 may be used in an LCD panel if the unit panel 12 is of a predetermined quality.
After the unit panels 12 (e.g., TFT array substrates and color filter substrates) are formed within their respective base substrates 11, a polyimide alignment layer is printed onto a surface of the base substrates 11 and a heat treatment is then performed. Next, an alignment direction is imparted to the polyimide alignment layer via a rubbing process whereby the surface of the polyimide layer is rubbed with a rubbing cloth. Accordingly, the rubbing process generates substantially straight alignment grooves on the surface of the polyimide alignment layer along a predetermined alignment direction. Next, the base substrates 11 are bonded together by a sealant provided at a periphery of the active regions 13 of the unit panels 12, wherein the sealant includes the liquid crystal injection inlet. Subsequently, the bonded unit panels 12 are separated from each other, liquid crystal material is injected through the liquid crystal injection inlet and into the cell gap between the TFT array and color filter substrates, and the liquid crystal injection inlet is sealed. Polarizing plates are formed on external surfaces of the bonded TFT array and color filter substrates and periphery circuits for driving the LCD panel are provided in the pad regions, thereby completing the assembly of the related art LCD panel.
FIG. 3 illustrates a plurality of unit panels in one base substrate and FIG. 4 illustrates a mask used to form the unit panels shown in FIG. 3.
Referring to FIG. 3, four unit panels 12, having the same size, are formed within a base substrate 11 and are spaced apart from each other by predetermined distances. When an intended size of the unit panels 12 is smaller than an actual size of the mask 16 shown in FIG. 4, the unit panels 12 may be designed by the mask 16. Accordingly, unit panels 12 may be formed within the substrate 11 by applying various process steps to portions of the base substrate 11 exposed by the mask 16, wherein the mask is relocated over the base substrate 11 four times. When, however, the intended size of the unit panels 12 is larger than the actual size of the mask 16, the unit panels 12 cannot be designed using the mask 16. Accordingly, unit panels 12 having a size larger than a size of a mask cannot be designed and large-sized LCD panels cannot effectively be designed. In order to overcome the problem, the size of the unit panels 12 must designed according to the size restrictions introduced by the mask 16.
As mentioned above, LCD devices are being used in applications requiring LCD panels of diverse sizes. Generally, the size to which an LCD panel is fabricated depends upon the size of the apparatus fabricating the LCD panel. Moreover, it is generally difficult to fabricate LCD panels of varying size in one fabrication processing line. Further, providing a plurality of fabrication processing lines, each suited to fabricate LCD panel of a particular size are not feasible as apparatuses used to fabricate LCD panels tend to be expensive and take up large amounts of space.
To minimize the aforementioned problems, a plurality of unit panels 12, each having the same size, may be formed within a base substrate 11, wherein the size of each unit panel 12 is one-half, one-third, one-quarter, or even substantially the same size of the size of the base substrate 11. However, when the size of one unit panel within a base substrate is a large-sized panel (e.g., having dimensions of at least 30 inches), other large-sized unit panels cannot be formed within the remaining portions of the base substrate. Accordingly, the efficiency with which the base substrate is used becomes reduced and the price of fabricating LCD panels increases.